Tips on Recoating Cured Epoxy Laminate?

Discussion in 'Fiberglass and Composite Boat Building' started by fly186, Jan 2, 2017.

  1. fly186
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    fly186 Junior Member

    I vacuum bagged my hardtop H80 Divinicell core with epoxy resin and 10oz eGlass on both surfaces 5 days ago. It was a big job but came out pretty good. I need to add another layer of either 10oz or 1708 biax in a few areas for more durability. I intend to sand the cured epoxy with 120 grit just until I scratch the glass and then wipe with some isopropyl alcohol or acetone before laminating these areas.
    Is that OK or should I do anything else to ensure a good bond?

    Thanks!
     
  2. PAR
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    PAR Yacht Designer/Builder

    Clean the surface with a little bit of soap and lots of water. When dry sand with 120, but you don't need to do more than scuff the surface. Removing epoxy isn't as necessary as just a good surface scratch. Finish sanding, wash again, before apply more goo and fabric. Solvents are okay on this wash, as there's no uncured amine left on the surface, as they were previously washed off after the cure. The is the appropriate epoxy, interlaminate, mechanical bond procedure.
     
  3. fly186
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    fly186 Junior Member

    Great info - thank you!
     
  4. jorgepease
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    jorgepease Senior Member

    I would wipe it down with Acetone to get rid of any wax before sanding. soap and water may not be enough. Whatever you do don't sand till you get that wax off
     
  5. upchurchmr
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    upchurchmr Senior Member

    Water is all that is required. Soap can help a little.
    Acetone is not required at all.
     
  6. PAR
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    PAR Yacht Designer/Builder

    More misconceptions to dismiss. Do NOT use solvents to remove a blush. Amine blushes are water soluble, not solvent soluble. If you use a solvent, you'll just spread and smear it around. The only time you use a solvent is after you've cleaned and abated the surface and need to "tack" it off, which you can do with a lightly solvent dampened cloth. I'd recommend you employ a real tack cloth, but if you must use a denatured alcohol dampened rag, as a tack cloth.
     
  7. jorgepease
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    jorgepease Senior Member

    I assume he vacuum bagged onto a waxed mold. If he doesn't use acetone to get that wax off his next layer is not going to bond. If he sands first, he is going to drive the wax down into the scratches
     
  8. PAR
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    PAR Yacht Designer/Builder

    Again, this is why you employ specific procedures. As previously mentioned, the surface is cleaned first (water and soap, for fresh epoxy), then abated, then cleaned again (solvents okay now), in prep for the next coating.
     
  9. fly186
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    fly186 Junior Member

    I washed the entire thing, top and bottom, with warm soapy water then rinsed well and dried. Next day started sanding.
    Will use acetone or denatured alcohol to remove all sanding dust before next lamination. Hopefully that should do it.
     
  10. endarve
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    endarve Junior Member

    Normally I sand small jobs but wiping Petit Skip Sand on epoxy worked for me when cold molding over a 42' cutter. It left a tacky surface and no sanding required other than to take the high spots off. No adhesion issues after years of use. I haven't used the stuff in a few years but Petit still says to use it on epoxy.

    E
     
  11. jorgepease
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    jorgepease Senior Member

    I remain skeptical that soap and water will effectively remove wax. When you wax your vehicle, you can wash it many times with soap and water and the wax remains, best of luck though.
     
  12. upchurchmr
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    upchurchmr Senior Member

    It technically Amine Blush - not actually wax.
    That is just a easy description by non chemists.

    Would you accept the Gougeons West System web site as an authority.
    They have been doing epoxy/glass/wood boats for at least 35 years.

    http://www.boatdesign.net/forums/fi...ng-cured-epoxy-laminate-57024.html#post794684

    Cured epoxy- Unless you're using WEST SYSTEM's blush-free 207 Special Clear Hardener, amine blush may appear as a wax-like film on cured epoxy surfaces. It is a by-product of the curing process and may be more noticeable in cool, moist conditions. Amine blush can clog sandpaper and inhibit subsequent bonding, but this inert substance can easily be removed.

    To remove the blush, wash the surface with clean water (not solvent) and an abrasive pad, such as Scotch-brite(TM) 7447 General Purpose Hand Pads. Dry the surface with paper towels to remove the dissolved blush before it dries on the surface. Sand any remaining glossy areas with 80-grit sandpaper. Wet-sanding will also remove the amine blush. If a release fabric is applied over the surface of fresh epoxy, amine blush will be removed when the release fabric is peeled from the cured epoxy and no additional sanding is required.

    Epoxy surfaces that have not fully cured may be bonded to or coated with epoxy without washing or sanding. Before applying coatings other than epoxy (paints, bottom paints, varnishes, gelcoats, etc.), allow epoxy surfaces to cure fully, then wash and sand.
     
  13. jorgepease
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    jorgepease Senior Member

    Im talking about the release wax from the mold )) not Blush. If you try to bond a - molded - product without first using solvent to clean it, the bond will fail. And if you sand first, the wax, which does stick to the molded part, gets driven into the scratches.
     
  14. upchurchmr
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    upchurchmr Senior Member

    My mistake. I agree.
     

  15. ondarvr
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    ondarvr Senior Member

    Acetone alone isn't a great product for removing wax or other contaminates from a surface.

    While acetone will dissolve many contaminates, it frequently dries too quickly for them to be removed from the surface, so what typically happens is one small speck or spot of some contaminate is smeared across the surface instead of being removed.

    Wiping a small area with acetone may work OK because you could do it couple times and hope the rag removed it from the surface, large areas are much more difficult.
     
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